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/// \file B1/src/PrimaryGeneratorAction.cc
/// \brief Implementation of the B1::PrimaryGeneratorAction class

#include "PrimaryGeneratorAction.hh"

#include "G4Box.hh"
#include "G4LogicalVolume.hh"
#include "G4LogicalVolumeStore.hh"
#include "G4ParticleGun.hh"    //使用G4ParticleGun作为粒子源
#include "G4ParticleTable.hh"  //包含Geant4粒子数据库
#include "G4SystemOfUnits.hh"  //包含Geant4单位制
#include "Randomize.hh"        //包含Geant4随机数产生器

namespace B1
{

    //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

    PrimaryGeneratorAction::PrimaryGeneratorAction()
    {
        ///在Geant4中一般用G4ParticleGun来创建粒子
        ///n_particle=1 表示在一个event中产生1个粒子, 可修改为其他数字以产生不同数量的粒子
        G4int n_particle = 1;
        fParticleGun = new G4ParticleGun(n_particle);

        /// default particle kinematic //创建粒子数据库G4ParticleTable对象以从中查找对应粒子
        G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();
        G4String particleName;
        //从创建的G4ParticleTable中查找名为"gamma"的粒子
        G4ParticleDefinition* particle = particleTable->FindParticle(particleName = "gamma");
        ///指定G4ParticleGun将要产生的粒子为刚刚查找到的alpha粒子
        fParticleGun->SetParticleDefinition(particle);
        fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0., 0., 1.));
        ///将alpha粒子的能量设置为 6 MeV
        fParticleGun->SetParticleEnergy(6.0 * MeV);
    }

    //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

    PrimaryGeneratorAction::~PrimaryGeneratorAction() { delete fParticleGun; }

    //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

    void PrimaryGeneratorAction::GeneratePrimaries(G4Event* event)
    {
        /// this function is called at the begining of ecah event
        /// In order to avoid dependence of PrimaryGeneratorAction on DetectorConstruction class
        /// we get Envelope volume from G4LogicalVolumeStore.
        /// 该成员函数将在每个event开始时被调用一次
        /// 为避免 PrimaryGeneratorAction 依赖于 DetectorConstruction 类,
        /// 我们从G4LogicalVolumeStore获取 Envelope(包络)体积.
        G4double envSizeXY = 0;
        G4double envSizeZ = 0;
        if (!fEnvelopeBox)
        {
            G4LogicalVolume* envLV = G4LogicalVolumeStore::GetInstance()->GetVolume("Envelope");
            if (envLV) fEnvelopeBox = dynamic_cast<G4Box*>(envLV->GetSolid());
        }

        if (fEnvelopeBox)
        {
            envSizeXY = fEnvelopeBox->GetXHalfLength() * 2.0;
            envSizeZ = fEnvelopeBox->GetZHalfLength() * 2.0;
        }
        else
        {
            G4ExceptionDescription msg;
            msg << "Envelope volume of box shape not found.\n";
            msg << "Perhaps you have changed geometry.\n";
            msg << "The gun will be place at the center.";
            G4Exception("PrimaryGeneratorAction::GeneratePrimaries()", "MyCode0002", JustWarning, msg);
        }

        constexpr G4double size = 0.8;
        /// G4UniformRand()产生0-1均匀分布的一个随机数, 平移到 -0.5到0.5 的均匀分布
        /// 再用 envSizeXY 缩放
        const G4double x0 = size * envSizeXY * (G4UniformRand() - 0.5);
        const G4double y0 = size * envSizeXY * (G4UniformRand() - 0.5);
        const G4double z0 = -0.5 * envSizeZ;

        fParticleGun->SetParticlePosition(G4ThreeVector(x0, y0, z0));

        // 使用 Gun 中接口, 指定本次Run中每个event开始时的粒子的产生信息
        fParticleGun->GeneratePrimaryVertex(event);
    }

    //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......

}  // namespace B1
